#include <stdio.h>

#define N 1000
int main() {
	int i, p, q, t, id[N];
	for (i = 0; i < N; i++) {
		id[i] = i;
	}
	while (scanf("%d %d\n", &p, &q) == 2) {
		if (id[p] == id[q]) continue;
		for (t = id[p], i = 0; i < N; i++) {
			if (id[i] == t) id[i] = id[q];
			printf("%d %d\n", p, q);
		}
	}
}
